Turning Your Amp On

Hey Jeff,
I’m a big fan of PG and I very much enjoy
reading your column. I’m in need of a little
advice. About six or seven years ago I purchased a Fender Hot Rod Deville 2x12. I
played this amp, on and off, for maybe a
year, bought a new house and packed the
amp away. I have not used this amp in four
or five years and now want to use it again.

I’ve spoken to some friends and have been
told I shouldn’t just “turn it on,” but that
there is a procedure I should follow. So I’m
writing this letter—and feeling quite stupid—to ask exactly how should I approach
turning this amp on. Please bear in mind
I’m not a technical person at all, so I ask
you to explain this as if you were speaking
to a four-year-old.

As stupid as this question may seem, I
thank you for shedding any light you can
on my dilemma.

Thanks,
Mike R.

Hi Mike,

Thanks for reading and for writing. As I tell
everyone, there are no stupid questions, so
I thank you for asking yours. Let me see if I
can shed a little light on this while trying to
remain as non-technical as possible.

The reason that your friends told you not to
just turn the amp on after it has been in storage so long has to do with the condition of
the electrolytic capacitors in the power supply circuit of the amplifier. I know that may
already be sounding complex, but I will do
my best to explain it as simply as possible.

The power supply in the amplifier converts
AC voltage from the wall (120VAC in the US)
to higher DC voltages which are needed to
power the internal circuitry of the amp. The
capacitors in the power supply are needed to
“smooth out” these voltages. The “smoother”
the voltages, the quieter the operation of the
amplifier (know that this is over-simplified, as
there are many other factors that determine
the noise level of an amplifier). If these electrolytic capacitors sit dormant for too long,
the insulation between the internal components can become minimized and the capacitor can begin to draw a considerable amount
of current. The result can manifest itself in a
couple of different ways.

The first, and I must say the less spectacular,
would be that they would cause the fuse to
blow. If you install a new fuse and try again,
you’ll get the same result. This would more
than likely cause you to either take the amp
to an experienced amp tech in your area, or
to put it back in the closet for another four
or five years, realizing that you didn’t really
need it anyway! The other and more colorful result would be to turn the amp on, turn
the standby on…crack, hiss, smoke! This is
because the capacitors, because of excessive
current draw, overheated and “vented.” Most
capacitors nowadays are manufactured with a
“vent” allowing them to discharge the internal pressure. If there was no vent, you would
simply substitute the “crack” with a “boom.”

Anyway, this is what can theoretically happen
when old, inactive capacitors are not properly
re-formed. The truth is though, I’ve seen many
newer amps that sat unused for quite a few
years be plugged in and turned on with no
adverse effects. That said, if you’re still looking
to play it safe I will give you a better way to go
about it, should you have the ability to so.

Obtain (beg, borrow, or buy) a piece of
equipment known as a Variac (also known as
a variable transformer or an autotransformer).
This is a variable transformer that plugs into
a wall outlet and will allow you to slowly
increase the AC line voltage applied to your
amplifier. [Ed. note: If you are not qualified to
work on amps, be sure to seek the supervision of a trained electrician—there are lethal
voltages involved here.] Start by removing
all the tubes in your amplifier (mark them
so you can reinstall them in the proper locations). Plug the Variac into the wall outlet
and plug your amplifier into the outlet on the
Variac. Set the Variac to zero volts. Turn on
the Variac, as well as the power and standby
switches on your amplifier. Raise the knob
on the Variac to approximately 10 volts. Wait
10 minutes and raise it another 10 volts. Do
this every 10-15 minutes or so until you reach
approximately 100 volts (note: you may not
see the pilot lamp begin to illuminate until
you reach the 50-60 volt range).

Once you reach 100 volts for 10 minutes,
return the Variac to zero volts and turn it off.
After a few minutes, unplug the amplifier from
the Variac and turn the power and standby
switches off. If during this procedure the fuse
has not blown, your amp is more than likely
fine. Reinstall the tubes, plug it in, turn the
power switch on, wait a minute or so, turn the
standby on and you should be good to go.

Good luck. Hopefully that will keep you from
having a Hot Rod Destruct.

Jeff Bober, one of the godfathers of the low-wattage amp revolution, co-founded and was the principal designer for Budda
Amplification. Jeff has just launched EAST Amplification. He
can be reached at pgampman@gmail.com

Jeff Bober is one of the godfathers of the low-wattage amp revolution. He co-founded and was originally the principal designer for Budda Amplification, though he launched EAST Amplification (eastamplification.com) in 2010. You can catch his podcasts at ampsandaxescast.com or email him at pgampman@gmail.com.

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